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Pear trees (Pyrus spp.), deciduous ornamental or fruiting trees, can grow 45 feet tall, and almost as wide. Pears grow in U.S. Department of Agriculture plant hardiness zones 4 through 11, depending on the species. They are spring-flowering, and the clusters of white blooms cover the tree. Pear trees also have bright red fall color. When problems occur with a pear tree, examining the environmental conditions can help reveal the cause.

Water and Pesticides

Inadequate water makes it difficult for trees to grow properly, and they may look sparse or stunted. During times of drought, pear trees need supplemental watering. Young trees normally need 1 inch of water a week, and double that during dry periods. Water mature trees three times a month during droughts. Pesticides and weed killers can cause leaves to be misshapen or drop if they've been used improperly. Follow label instructions when using pesticides. Do not spray when it's windy to keep pesticides from drifting onto trees.

Transplant Stress

New pear trees arrive from the nursery with their roots cut. During the first two years after planting, the root system is working to catch up to the size of the canopy. During this time, the leaves will be smaller and less frequent. They may also begin to show fall coloring in late summer, and the leaves may drop early. Water the tree regularly and deeply for the first five years of growth to help the root system develop.

Aphids and Pear Psylla

Aphids feed on the leaves of pear trees. In large numbers, they cause leaves to curl or distort, making them appear smaller. The aphids can also cause stunted shoot growth so there are fewer leaves. If aphids are present, there will be black soot and honeydew on the tree. Insecticidal soap or ladybugs can help control aphids. Pear psylla are tiny winged insects that carry an organism that causes pear decline. The decline causes rolled leaves, smaller leaf size and early leaf drop. Apply oil sprays to kill the psylla. Water and fertilize the tree properly to reduce tree stress.

Fire Blight and Bacterial Leaf Scorch

Fire blight and bacterial leaf scorch are similar in appearance. In both cases, the leaves turn brown. Fire blighted leaves stay attached to the tree, while the leaf scorch-infected leaves drop. This makes the leaves seem sparse, as only healthy leaves remain on the tree. Fire blight starts at the branch tip and spreads inward. Bacterial leaf scorch leaves healthy buds on the branch though the leaves die. Both can be treated if you notice them quickly. Remove and destroy infected limbs of fire blight-damaged trees.

About the Author

Jill Kokemuller has been writing since 2010, with work published in the "Daily Gate City." She spent six years working in a private boarding school, where her focus was English, algebra and geometry. Kokemuller is an authorized substitute teacher and holds a Bachelor of Arts in English from the University of Iowa.